How to make a thin sphere with a hole?
If you use booleans, use solid meshes as cookie cutters, not planes. A cylinder maybe.

Inverted normals and an inner surface are indeed a good idea.


Also kill any selection and hit my favorite shortcut: CTRLALTSHIFTM to check for any problems with the mesh. Ideally no verts or edges should get selected. Booleans like perfect watertight topology. Just like 3D printers.

Then you can subtract the cylinder and have holes in your egg shell.



Or you simply delete a few edgerings, select the rim and connect them with the bridge tool.